Computer systems often contain one or more integrated circuit (IC) chipsets that are coupled to memory modules using a memory interface. The memory interface provides communication between the IC chipset such as a central processing unit (CPU) and the memory modules. The memory interface may include address bus-lines, command signal lines and data bus lines.
Initially, each memory module was made up of a single substrate with memory chips on one or both sides. However, increasing demand for high computer performance and capacity resulted in a demand for a larger and faster memory. To meet this demand single memory modules having two or more electrically connected substrates mounted substantially parallel to each other were developed. U.S. Pat. No. 5,949,657 discloses an example of this type of memory module. Besides multiple substrate memory modules, memory density was increased by stacking memory chips on the same substrate. U.S. Pat. No. 6,487,102 discloses an example of this chip stacking technique.
However, as the operating speed and number of memory modules and/or memory chips connected to the chipset increase, the increase in capacitive load may place a substantial limit on the amount and speed of the memory. To relieve these capacitive load effects, memory modules having a buffer or register to buffer the command and address lines were developed. Here, each substrate of the module includes such a buffer for relieving capacitive load effects. Again U.S. Pat. No. 6,487,102 provides an example of what is commonly referred to as a registered memory module.
More recent advances in memory modules have provided fully buffered memory modules. In a fully buffered memory module, the command and address lines associated with the memory chips of each substrate are buffered as in the registered memory modules, and another buffer on each substrate of the module buffers the data lines. Fully buffered memory modules are said to electrically isolate the memory module from the chipset. U.S. Pat. No. 6,553,450 discloses an example of a fully buffered memory module.